Update

exercises.md

@@ -99,6 +99,8 @@ TODO: tetris, voice synth?, snake, quadratic equation, fractals, 2D raycasting,
 
 Here are some questions to test your LRS related knowledge :D Questions here are of varying difficulty, areas and may potentially have even multiple solutions, just like in [real life](irl.md).
 
+Bear in mind the main purpose of this quiz is for you to test your understanding of things AND possibly learn something new or spark some curiosity -- don't rage if you get something wrong or if maybe the question is worded badly (which can happen) or even if the answer here has an error or something (which can also happen), the important thing is you gain new knowledge, if only something like "oh, this is a thing" or "this is a nice kind of problem I haven't seen before" etc.
+
 1. What's the difference between *[free software](free_software.md)* and *[open source](open_source.md)*?
 2. Use numbers 1, 3, 4 and 6, each exactly once, with any of the basic arithmetic operations (addition, subtraction, multiplication, division) and brackets to get the result 24.
 3. Name at least 10 different [programming languages](programming_language.md).
@@ -145,7 +147,13 @@ Here are some questions to test your LRS related knowledge :D Questions here are
 44. Name at least two TCP/IP or OSI [network](network.md) layers: about each shortly explain its purpose, addressing and at least one protocol of this layer.
 45. We know [HTTPS](https.md) is shit because it's [encrypted](encryption.md) and requires [certificates](certificate.md). Explain what these certificates are, why HTTPS needs them, how their absence could be "abused" and who issues them.
 46. We have two barrels, one with water, one with wine, each having the same amount of liquid. We take a cup, fill it with water from the water barrel, pour it over to the wine barrel, mix it up, and then we fill the same cup with this mixture of water and wine from this barrel and pour it back to the water barrel. Both barrels now have the same amount of liquid again, but the liquids are mixed. What percentage of water is in the water barrel and what percentage of wine is in the wine barrel? Find a general formula for a cup of any size.
-47. Did you enjoy this quiz?
+47. In context of programming languages explain the difference between *[lvalue](lvalue.md)* and *[rvalue](rvalue.md)* -- Where do they appear? What are they? How do they differ and what conditions are placed on each? Also place each of the following expressions under these categories (i.e. say which are lvalues, rvalues or both; details may depend on programming language, so just comment on that): `123`, `someVariable + 123`, `someArray[20]`, `*(somePointer + 4)`, `someVariable`.
+48. Which start is the closest to [Earth](earth.md)?
+49. A symmetric [relation](relation.md) is that for it hold that if A is in relation with B, then also B is in relation with A (for example "is married to"). Antisymmetric relation is that for which it holds that if A is in relation with B and A is distinct from B, then B is NOT in relation with A (for example "is parent of"). Give an example of relation that is both symmetric and antisymmetric.
+50. Is [LGBT](lgbt.md) [good](good.md)?
+51. Write a [C](c.md) function in 60 characters or fewer that takes a string (`char *`, consider zero terminated ASCII string) and replaces all semicolons in it with colons (`;` -> `:`). It can return nothing (`void`).
+52. Order the following [people](people.md) by date of their birth from oldest: [Alan Turing](turing.md), Caesar, [Buddha](buddha.md) (Siddhartha Gautama), Johannes Gutenberg, Aristotle, [Charles Babbage](babbage.md), [Linus Torvalds](torvalds.md), [Jesus](jesus.md), [Adolf Hitler](hitler.md), Muhammad (prophet of Islam), [Albert Einstein](einstein.md), [Richard Stallman](rms.md), Napoleon, Leonardo da Vinci, [Karl Marx](marx.md).
+53. Did you enjoy this quiz?
 
 ### Answers
 
@@ -195,7 +203,13 @@ Here are some questions to test your LRS related knowledge :D Questions here are
 44. For example: application layer (highest level layer, concerned with applications communicating with each other, addressing by ports, protocols: HTTP, Gopher, FTP, DNS, SSH, ...), transport layer (middle level layer, concerned with delivering data over a potentially unreliable channel, implements establishment of connection, handshakes, reliable delivery, delivering in correct order etc., protocols: TCP, UDP, ...), network layer (below transport layer, concerned with delivering packets over a network, implements routing, forwarding etc., addressing by IP addresses, i.e. numerical machine addresses, protocols: IPv4, IPv6, ...), OSI physical layer (lowest level layer, concerned with sending bits between two directly connected devices, works with frequencies, electronic circuits etc., no addressing, protocols: ethernet, USB, Bluetooth, ...), ...
 45. Certificate is a file that contains the domain's public key (needed to communicate using asymmetric cryptography) that is [digitally signed](digital_signature.md) by some "trusted authority", a business that declares itself to be trusted and lets itself be paid for cryptographically confirming that public keys belong to specific servers. Without certificates a [man in the middle](man_in_the_middle.md) "attack" could be performed in which a middle man could sneakily swap a public key that's being transmitted for his own public key which would then allow him to listen to the unencrypted communication.
 46. Let's say both barrels hold 1 unit of liquid volume at the beginning, *n* is the portion of one barrel we'll be pouring over (e.g. *n = 4* means 1/4th of a barrel), *x* is water, *y* is wine. At beginning we have the following in respective barrels: *x* and *y*. After first pour over we have: *x - x/n* and *y + x/n*. After pour back we'll have: *x - x/n + (y + x/n)/(n+1)* and *y + x/n - (y + x/n)/(n+1)*. Note: the division by *n + 1* is important, dividing by *n* would be an error (we are taking away a part of barrel that is over its original capacity). Now we can just simplify the expressions to see the amount of water and wine in each barrel, i.e. we'll get: *x * (1 - 1/n + 1/(n^2+n)) + y * 1/(n+1)* and *x * (1/n - 1/(n^2+n)) + y * (1 - 1/(n+1))*. So for example amount of water in the first barrel is *1 - 1/n + 1/(n^2+n)* which simplifies to *n/(n+1)* -- that is also the exact amount of wine in the other barrel (*1 - 1/(n+1)* simplifies to the same expression). So the answer is there is *n/(n+1)* of the barrel's original liquid (and 1 minus that of the other). Logically we see the purity of each barrel has to be the same just because of the conservation laws.
-47. yes
+47. The details may differ from language to language, but generally *lvalues* and *rvalues* appear in assignment commands -- lvalue is any value or expression that may appear on the left side of assignment, rvalue is that which may appear on the right. For example in `myVariable = x + 4` the left side, `myVariable`, is lvalue, and the right side, `x + 4`, is rvalue. From this follow the conditions on lvalues and rvalues, i.e. rvalue must be something that returns some computed value and lvalue must be something that identifies a place where a value can be stored -- sometimes an expression can be both lvalue and rvalue at the same time. Examples: `123` is rvalue, `someVariable + 123` is rvalue, `someArray[20]` is both lvalue and rvalue, `*(somePointer + 4)` is also both and `someVariable` is both too.
+48. The Sun. Some people get tricked here, not realizing Sun is a star.
+49. For example "is equal to" or empty relation (no element is in relation with any other). For such a relation it must generally hold that any element may only be in relation with itself.
+50. hell no
+51. For example: `void r(char *s) { while (*s) s += (*s -= *s == ';') != 0; }`;
+52. Buddha (< -480), Diogenes (-404), Aristotle (-384), Caesar (-100), Jesus (around -5), Muhammad (around 570), Gutenberg (around 1400), Da Vinci (1452), Napoleon (1769), Babbage (1791), Marx (1818), Einstein (1879), Hitler (1889), Turing (1912), Stallman (1953), Torvalds (1969).
+53. yes
 
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